Data syncing in a distributed system

A method comprising:

• receiving, at a replica server, a start replication message from a source system to replicate data of a source volume to a replicated volume on the replica server, wherein the replicated volume comprises a copy of data of the source volume, and wherein the source system forwards input/output (I/O) requests to the replica server after the start replication message is sent;
• initiating a data structure associated with units of data of the replicated volume;
• receiving, from the source system, a write request comprising write data associated a unit of data of the replicated volume, wherein the source system wrote the write data to the source volume based upon the write request;
• writing the write data to the replicated volume;
• updating the data structure to indicate the write data has been written after the receipt of the start replication message;
• receiving source metadata associated with the source volume, wherein the metadata comprises an ordered list of block identifiers for data blocks of the source volume, and wherein each block identifier is used to access a data block;
• comparing the source metadata with prior metadata associated with a prior point-in-time image of the source volume to determine blocks of data that have changed since the prior point-in-time image of the source volume;
• determining, using a processor, a first block of the blocks of data should not be retrieved based upon the data structure;
• determining a second block of the blocks of data should be retrieved based upon the data structure;
• retrieving the second block from the source system;
• and
• writing the second block to the replicated volume.

A non-transitory computer-readable medium having instructions stored thereon, the instructions comprising:

• instructions to receive a start replication message from a source system to replicate data of a source volume to a replicated volume on the replica server, wherein the replicated volume comprises a copy of data of the source volume, and wherein the source system forwards input/output (I/O) requests to the replica server after the start replication message is sent;
• instructions to initiate a data structure associated with units of data of the replicated volume;
• instructions to receive, from the source system, a write request comprising write data associated a unit of data of the replicated volume, wherein the source system wrote the write data to the source volume based upon the write request;
• instructions to write the write data to the replicated volume;
• instructions to update the data structure to indicate the write data has been written after the receipt of the start replication message;
• instructions to receive source metadata associated with the source volume, wherein the metadata comprises an ordered list of block identifiers for data blocks of the source volume, and wherein each block identifier is used to access a data block;
• instructions to compare the source metadata with prior metadata associated with a prior point-in-time image of the source volume to determine blocks of data that have changed since the prior point-in-time image of the source volume;
• instructions to determine a first block of the blocks of data should not be retrieved based upon the data structure;
• instructions to determine a second block of the blocks of data should be retrieved based upon the data structure;
• instructions to retrieve the second block from the source system;
• and
• instructions to write the second block to the replicated volume.